This chapter is the first of three that centre upon Nietzsche’s critique of pessimism in his mature philosophy of the 1880s. It presents Nietzsche’s psychological critique of pessimism as symptomatic of a particular calibration of one’s ‘drives’ that produces fatigue and a world-directed ressentiment. The chapter gives special attention to the crucial similarities and differences between Nietzsche’s psychological reduction of pessimism and those of the degeneration theorists, and the English psychologist James Sully, arguing that Nietzsche’s own position is subtly unique and, in some ways, more plausible. The final sections of the chapter address (1) Nietzsche’s diagnosis of Christianity as the pinnacle manifestation of pessimistic sentiment and (2) the problem of the ‘scope’ of Nietzsche’s psychological reduction.